1. Field of the Invention
This invention relates to device processing and, in particular, to semiconductor processing.
2. Art Background
The etching of a first material without unacceptably removing or damaging a second is often required in processes such as semiconductor device fabrication procedures. For example, it is desirable in certain situations, such as in the production of appropriately configured gates, to remove a region of silicon and/or metal silicide without causing unacceptable removal of an underlying or adjacent region of a silicon oxide, e..g, silicon dioxide. Processes such as plasma etching and reactive ion etching employing a chlorine-containing gas are often utilized to accomplish these results. In these techniques, a chlorine-containing gas is typically introduced in proximity to the body to be etched, and a plasma is established in the gaseous medium by applying r.f. power between electrodes. Typically, the substrate rests on the powered electrode, and the DC electric field associated with this electrode directs the energetic entities produced in the plasma (e.g., ionized molecular fragments, ionized molecules, and ionized atoms) towards the substrate and, through various mechanisms, causes removal of the impacted material.
A variety of etching apparatus geometries and processing conditions has been employed in the dry etching of materials such as silicon. The specific configuration and etching conditions are generally chosen to yield etching characteristics tailored to the particular semiconductor device fabrication application. For example, a hex reactor, e.g., an apparatus disclosed in U.S. Pat. No. 4,298,443, issued Nov. 3, 1981 (which is hereby incorporated by reference), and illustrated in the Figures of this patent, is capable of processing a large number of substrates during one etching procedure. This reactor includes a hexagonally shaped cathode contacting the substrates and typically a grounded outer shell that functions as the second electrode. A plurality of substrates is positioned on each face of the hexagonal cathode. Thus, for example, if 4 substrates are placed on each face, it is possible to process 24 substrates during one etching procedure. Alternatively, parallel plate reactors, i.e., reactors having a cathode and anode each formed by a plate whose major surfaces are held in a parallel configuration, have been advantageously employed in less demanding applications to provide suitable simultaneous etching of 4 to 6 substrates. In a third type of reactor, one substrate covers essentially the entire r.f. driven electrode, and a second electrode, e.g., a parallel plate or vessel component, is provided.
While in many situations etching involving plasma-generated energetic entities is advantageously employed, it is not without associated difficulties. For example, the use of a plasma often leads to the deposition of contaminating materials on the substrate surface. These contaminating materials such as metals from the reaction vessel or substrate holder, e.g., aluminum, either degrade device properties or hinder subsequent processing procedures. Various measures have been employed to avoid such contamination. For example, in the case of a hex reactor, a tray surfaced with a material, e.g., a polymer such as a polyarylate, is positioned on each face of the hex cathode with openings through which the substrates are inserted. Thus, the substrates contact the underlying electrode while remaining exposed to the plasma environment.
Although as presently practiced, dry etching yields excellent results with limited shortcomings, new applications have produced further, yet unsatisfied, demands. For example, there are many applications of emerging importance that require the removal of materials such as silicon with the effect on adjacent, e.g., underlying or coplanar, materials such as silicon dioxide substantially reduced from that which has been previously achieved. For typical etching systems, selectivity, i.e., the rate of etching of the desired region relative to underlying or unmasked adjacent regions of different compositions, is not greater than 30 to 1. However, as packing density in electronic devices, e.g., integrated circuits, increases, many situations are evolving which require selectivities of at least 50, preferably at least 70, and most preferably at least 100 to 1. For example, in the etching of TaSi.sub.2 /polycrystalline silicon composite gates, selectivity on the order of 100 to 1 is required to assure that the thin oxide, less than 250 Angstroms thick, which is used as an etch stop will not be totally removed.
Despite the substantially increasing desire for higher selectivity, the adjusting of dry etching apparatus configuration and processing conditions to achieve such results has not been reported. Indeed, in the dry etching of materials employed in semiconductor devices, often the adjusting of conditions or configurations to achieve one result causes a substantial problem in a second unrelated etching characteristic. Thus, although there is a desire for selective, plasma dry etching procedures, i.e., procedures involving a gas plasma with selectivities greater than 50, such techniques have not as yet been reported.